Method of anchoring wire bundles for prestressed concrete constructions



Oct. 22, 1963 A. BRANDESTINI METHOD OF ANCHORING WIRE BUNDLES FORPRESTRESS CONCRETE CONSTRUCTIONS 3 Sheets-Sheet 1 Filed July 1, 1959Ammo snmssmi w arm, 41.x, Mam Z1 3,107,983 PRESTRESSED- Oct 22, 1963 A.BRANDESTINI 7 METHOD OF ANCHORING WIRE BUNDLES F OR CONCRETECONSTRUCTIONS .3 Sheets-Sheet 2 Filed July 1, 1959 m vgmpon ANT NIO BRnlvoss'rml 1963 A. BRANDESTINI 3 7,

. 9 METHODOF ANCHORING WIRE BUNDLES FOR PRESTRESSED CONCRETECONSTRUCTIONS Filed July '1, 1959' .5 sheets-sheet s Fig. 11 20 K I" l JQ 21 1b A v Q A- I v l 21 1b ig.1.?

1c Fig-1 MENTOR Aurowo BIMNDESTINI by v WM MQPWM hired rates The presentinvention rel-ates to a method of anchoring wire bundles for prestressedconcrete constructions by means of anchor bodies engaging the ends ofeach bundle.

Today quite a number of methods are known, in which entire wire bundlesare prestressed and subsequently secured at their ends in anchor bodiesbearing against the concrete construction. The wire bundles usuallyconsist of parallel, high-quality steel wires having a diameter from to8 mm. and a circular or oval cross-section. The anchoring of theindividual wires in the anchor bodies is brought about either by wedgingaction or by upsetting the wire ends. All these methods have thedisadvantage that relatively expensive anchor bodies must be used, whichremain in the construction and increase the costs thereof. In order toreduce these anchoring costs, anchors have been already proposed, whichhave comparatively small dimensions. After the wire bundle has beenprestressed, these small anchors are housed in a recess of theconstruction, whereupon mortar is pressed into the recess and in turn isencircled by a surrounding wire spiral. After the pressure-insertedmortar has hardened, the anchor bodies are supported by the hardenedmortar. Such a solution has been disclosed for the first time in FIG. 7of the Swiss Patent No. 279,562. The mortar pressed into the recessserves as bearing surface for the anchor bodies, which also in this caseremain within the construction.

It is an object of the present invention to provide a more economicalmethod of producing prestressed concrete.

The method according to the invention consists in that the ends of thewires of the wire bundle, situated in a terminal recess of the concrete,are first anchored on the associated anchor body, whereupon the wirebundle is prestressed and mortar is forced into the recess at the rearof the anchor body, and then the anchor body is removed after the mortarenclosing the wires has hardened, so that the wires of the bundle areanchored solely by adhering to the hardened mortar.

It has been already general practice in the so-called prestressedbedding technique, known in Wire bundle anchorings for prestressedconcrete constructions, to directly anchor, solely by adhesion of theconcrete of the building construction, particularly wires havingacomparatively small diameter and especially profiled or fiat wires,without the use of end anchors. This tension bedding method, however,has considerable disadvantages in comparison with the method accordingto the invention, in which no tension bedding is used. The tensionbedding method thus requires long tension tracks, at the ends of whichthe individsal prestressed bundles must be secured prior to theintroduction of the concrete. In the method according to the inventionsuch tension tracks are not required, since the prestressing force isdirectly transmitted to the hardened concrete construction.

The method according to the invention may include the additionalprovision of severing the wire ends behind the anchor body, after themortar enclosing the wires has been hardened, to facilitate the removalof the anchor body.

The present method may also include the supplemental steps, for thepurpose of increasing the adhesive ability,

atent Bdh'lfibd Patented Get. 22, 1963 ice n, is

that prior to the tensioning of the wire bundle, at least the Wirebundle section located in the terminal recess of the concreteconstruction is provided with obstructing means in such manner thatlongitudinally spaced portions of this bundle section have across-section differing from the adjacent bundle cross-sections.

The present invention will now be described more fully with reference tothe accompanying drawings illustrating, by way of example, severalembodiments of the invention, and in which:

FIGURE 1 is the end of a wire bundle having an anchoring body associatedtherewith,

FIGURE 2 shows the end of a wire bundle resting against the concreteconstruction by means of the anchor body,

FIGURE 3 shows the wire bundle end after the mortar has been pressed in,

FIGURE 4- indicates the wire bundle end together with a device for theremoval of the small heads of the Wires,

FIGURE 5 is the end of the wire bundle anchored by adhesion afterremoval of the anchor body,

FIGURE 6 shows the end of a wire bundle after said bundle has beenrprestressed,

FIGURE 7 shows the wire bundle end after the injected mortar has beenhardened and prior to the removal of the anchor body,

FIGURE 8 is the completed anchoring of the wire bundle after the anchorbody has been removed,

FIGURE 9 is an example of a wire bundle end anchored by the adhesiveaction of the hardened mortar,

FIGURE 10 illustrates a further example of a Wire bundle end firmlyanchored by adhesion, and

FIGURES 11 to 14 show each an example of a bundle wire.

In the example shown in FIGURES 1 to 5, the wire bundle consists of aplurality of high-quality steel wires 1, which are enclosed by a tubularcasing 2. The wire ends are passed through cylindrical holes of acylindrical externally threaded anchor body 3 which has a threaded,central bore (FIGURE 1). Then, small anchoring heads 4 are produced onthe ends of the wires by a cold upsetting operation. The wire bundle,thus encased and provided with the anchor body 3, is subsequently placedin known manner into the casing or boarding of the concreteconstruction, whereupon concrete is filled in. During this concretingoperation, the wire bundle end carrying the anchor body 3 is situatedwithin a recess 5, which is formed by an enlarged end portion 7 of thetubular casing 2 located at the end of the built construction 6.

The wire bundle is now tensioned by means of a suitable, e.-g. hydraulicor pneumatic traction device not shown acting on a spindle 8 which isscrewed into the central threaded bore of the anchor body 3. The smallanchor heads 4 then will abut against the outer frontal surface of theanchor body 3, which in turn is pulled out of the recess 5. The anchorbody 3 is supported upon the front face of the hardened concreteconstruction 6 by means of a nut 9 screwed on the anchor body 3 and awasher 10 (FIGURE 2). After removal of the tensioning device mortar 11is forced into the recess 5 through the central bore of the anchor body3. The mortar ll encloses the end portion of the wire bundle in closecontact with the wires. After the mortar has hardened, the wires 1firmly adhere to the mortar (FIGURE 3). Since the diameter of the anchorbody 3 for the reception of a plurality of wires 1 must necessarily belarger than the diameter of the bundle lying within the tubular casing2, the Wire ends diverge within the recess, i.e. the wire ends leavingthe tubular casing 2 spread apart towards the anchor body 3 to a bundlediameter, which is greater in comparison with the internal diameter ofthe tubular casing, so that these wire ends will be accessible from allsides for the mortar ll. forced into the recess 5. Thereby a perfectadhesion of the wires to the mortar is obtained. A device 12, which maybe e.g. a grinding or milling device, is now placed against the anchor 3and operated to remove the small anchor heads 4 on the ends of the wires(Pi URE 4). The anchor body 3 together with nut and washer lit) can nowbe taken away, so that none of the original anchoring elements remainsin or on the concrete construction (FIGURE 5).

The removal of the small anchor heads may also be effected by onlypartly grinding off the latter and subsequently extracting the anchorbody under corresponding deformation of the remaining portion or" thesmall anchor head.

In case a dismountable anchor body is used, the small anchor heads onthe wires have not to be removed. In this case a lo-werable abuttingdevice is arranged in place of the washer It after the mortar hashardened this device will be lowered, whereafter the nut 9 is removedand the anchor body, by disassembling the latter, is taken off.

The wire bundle can also be anchored in a Common anchor body by meansor" a wedge and secured to the concrete construction after tensioning bymeans of a lowering device. After hardening of the mortar the loweringdevice is moved downwards, the wedge thus relieved is removed and theanchor body can be withdrawn.

The method according to the invention also permits the use of curvedwire bundles, which fact in many cases represents a static advantage.The casing for the concrete construction according to the describedmethod can be removed again rapidly, i.e. prior to the prestressing ofthe concrete; it thus may be used several times. The production of aplurality of similar constructions, e.g. several similar beams orgirders, requires only the provision of a single casing. The describedmethod can be applied for the production of prestressed concrete girdersdirectly on the building-site, since no larger installations, such asfor example a tensioning bed, are required.

In the embodiment shown in FEGURES 6 to 8, the wire bundle consists of aplurality of high-grade steel wires 1, which are enclosed by a sheathingnot shown. The wire ends are secured to an anchor body 3 in a mannerknown per se passing them for instance through cylindrical holes of theanchor body and providing them with upset small anchor heads, which abutagainst the anchor body, when the bundle is subjected to tension. Thebundle provided with the sheathing and the anchor body is then placed inthe casing for the concrete construction, whereupon the concrete work iseffected. After the bundle has been prestressed, during which operationthe anchor body is pulled away from the concrete construction 6 and thewire end portions protrude out of an end recess 5 present in theconcrete construction, the anchor body is temporarily supported on thehardened concrete structure 6 by means of a supporting bracket 13, whichthrough the intermediary of a lateral aperture 14 affords free access,at least from one side, to the wire portions situated between anchorbody 3 and concrete construction 6. Thereafter, mortar 11 is forced intothe recess 5, which mortar closely surrounds the wire portions containedtherein. After the mortar 11 has been hardened, the 'WllfiS 1 contactingsaid mortar firmly, adhere to the latter (FIGURE 7) and the anchor body3 can now be removed. For this purpose the wire ends behind the anchorbody 3 are severed by means of a cutting torch passed through thelateral aperture 14 of the supporting bracket 13. When no two wire endsshall project from the completed concrete structure (not as shown inFIGURE 8), then the cut of the burner naturally may be guidedimmediately along the front surface of the concrete construction 6, sothat the wire ends are cut off flush with that surface.

In place of a cutting torch 15, any other cutting or grinding tool mayalso be employed for severing the wire end portions anchored on theanchor body 3.

The losses of wire material entailed through severing the Wire ends arevery low, While the cutting operation can be carried out rapidly and aclean cut is obtained without requiring any complicated equipment.

In order to insure a perfect bedding of thewire portions, located in therecess 5 of the concrete structure 6, within the pressure-insertedmontar, these wire end portions can be slightly spread apant from eachother starting at the tubular sheath. On the other hand, the bundleportion housed in the recess 5 may be provided with obstructions inorder to improve adhesion; thus wire strands, profiled or upset wiresmay be used, or this bundle portion may be twisted, or spread severaltimes in spaced intervals and again combined.

in the example shown in FIGURE 9 the wire bundle consists of a pluralityof high-grade steel wires 1 which are surrounded by a tubular sheath,not shown. After the wire ends have been secured to an anchor body andplaced into the casing for the concrete construction in a manner knownper se, it is concreted, a recess 5 being produced in the zone of thewire bundle ends by an enlarged end portion of the tubular casing. Thewire bundle sec tion, which will be placed into this recess after thebundle has been prestressed, is provided with obstructing means,improving the adhesion of this bundle section, prior tothe insertion ofthe bundle into the casing and prior to the application of the anchor.In the embodiment according to FIGURE 9, for the provision of the saidobstructing means longitudinally spaced perforated plates 16 areprovided, having holes spaced apart from each other a relatively greatdistance, through which holes the wires are passed and thus are spreadapart with respect to the wires in the bundle situated in the tubularsheath, while the bundle section located between two adjacent perforatedplates 16 is again constricted by a suitable lacing 17. The perforatedplates 16 may consist of sheet metal. By means of the described repeatedspreading and contrioting of the bundle, the cross-section thereof ischanged several times within the recess 5, whereby the adhesion isconsiderably improved in comparison with the parallel-wired bundle,having the same cross-section throughout its extent.

In the embodiment of the invention shown in FIGURE 10 the obstructingmeans, which cause a variation in cross-section of the bundle lengthsituated in the terminal recess 5 of the concrete structure 6, areformed by small upset heads 18 and auxiliary anchor plates 19. Beforethe bundle is brought into the casing for the concrete structure the endportions of the wires protruding out of the tubular sheath are passedthrough perforations of a first auxiliary anchor plate 19, whereby thebundle is spread, due to the relatively wide spacing of the perforationsin the plate, with respect to the bundle cross-section in the tubularsheath, whereupon small heads 18 are upset on the wires 1; in thedescribed example the end portions of the wires are subsequently forcedthrough the holes of a second auxiliary anchor plate 19, which is spacedsome distance apart from the first plate 19, and provided withadditional small upset heads 18 in front of this plate. plates 1? couldalso be arranged. The auxiliary anchor plates can be formed byrelatively thin sheet metal. Also in this case, the anchor plates 19cooperating with the small heads 18 form obstructing means, by which thebundle cross-section at these points is so modified with re spect to theadjacent cross-sections, that a considerable improvement of the adhesivepower of the Wire bundle in the concrete 11 will be obtained.

Obstructions, causing a sectional variation of the bundle lying in theterminal recess 5, can also be produced by twisting or interlacing thisbundle portion. Moreover, the individual wires of the bundle themselvesmay be Naturally, more than two auxiliary anchor V provided with suchobstructing and retaining means. Examples of such wires are illustratedin FIGURES 11 to 14. As shown in FIGURE 11, the Wire 1a is provided withclosely spaced upset portions 20. The wire 1b according to FIGURES l2and 13 includes compressed flattened portions 21 for the same purpose.Finally, FIG- URE 14 shows a wire '10 formed as stranded unit.

After the necessary retaining and bonding expedients have been providedon the wire bundles in the manner described, either throughsupplementary application of auxiliary elements, through deformingoperations, or by means of suitable selection of profiled wires, andafter the ends of the bundle have been fitted with an anchor body, thebundle is placed into the casing for the concrete structure andprestressed after concreting. The anchor body, not shown, which servesfor the provisional support of the tensioned bundle on the concreteconstruction is removed after the mortar forced into the terminal recess5 has hardened, so that the bundle remains anchored in stressedcondition exclusively by adhering to the pressure-inserted mortar. Theremoval of the anchor body can be brought about by severing the wiresimmediately behind the anchor body, e.g. by means of a cutting burner ora grinding disk. When the wires are secured to the anchor body by meansof small upset heads, then for removing the anchor body only the smallanchoring heads may be ground away or, afiter preliminary grinding,broken oh.

I claim:

A method of anchoring wire bundles for prestressing concrete structures,by means of anchor bodies each engaging the wire ends of one bundlesituated in a terminal recess of the concrete structure, comprising thesteps of temporarily anchoring the Wire ends of the bundle of wires onthe associated anchor body provided with a plurality of cylindricalperforations, by passing each Wire of the bundle through one perforationof the anchor body and then forming a head at each wire end by a coldupsetting operation, prestressing the wire bundle while having saidheads abut against one face of the anchor body, forcing mortar into saidterminal recess at the rear of the anchor body, removing said heads onthe wire ends when the mortar in said recess has set, and taking off thean chor body from the wire ends, whereby the Wires of the bundle areanchored solely by adhering to the hardened mortar in said recess, saidheads on the wire ends being at least partly removed by a grindingoperation when the mortar has set in said terminal recess, and then theanchor body is pulled oif from the wire ends by deforming the remainingportions of the heads.

References Cited in the file of this patent UNITED STATES PATENTS2,371,882 Freyssinet Mar. 20, 1945 2,787,042 Brequet Apr. 2, 1957FOREIGN PATENTS 683,920 Great Britain Dec. 10, 1952 694,596 GreatBritainJuly 22, 1953 707,144 Great Britain Apr 14, 1954 162,861 Australia May16, 1955 162,538 Australia Apr. 20, 1955 206,834 Australia Mar. 6, 1957

